M&C Saatchi beat Fallon and JWT in the final pitch, ending a review process that began in January.
The agency will be responsible for handling a global integrated campaign to support the launch of a new handset.
Carrie Hindmarsh, managing director of M&C Saatchi, said: "This is a great win for us. Vertu is an international luxury brand and truly unique. We look forward to being part of the exciting plans they have for the future."
Vertu has used a number of agencies to develop past campaigns, including DHM, Black Sun and Dave. MediaCom handles the brand's media planning and buying activity.
Launched in 2000, Vertu's luxury mobile phone handsets are sold in jewellery shops and department stores across almost 50 countries.
Vertu's most recent campaign, created by DHM, launched at the end of 2009 in key global markets, and featured the actress Michelle Yeoh and motorsport boss Jean Todt, using the strapline "Life beautifully arranged".
Prasad Menon, global marketing director at Vertu, said the appointment of a single agency was "a response to Vertu’s changing needs and requirements", and that M&C Saatchi was chosen for its "commercial sensibilities in taking the brand to the next phase".